The dirtiest thing in your kitchen is the thing you clean with
A used kitchen sponge can carry up to 54 billion bacteria in a single cubic centimetre. Boiling it doesn't fix that.
In 2017, researchers in Germany collected 14 used kitchen sponges from ordinary homes and ran the bacteria inside them through DNA sequencing. They found up to 54 billion bacterial cells in a single cubic centimetre, a density normally seen in samples from the human gut.
Most of those bacteria are harmless, but not all. Several belonged to groups that can cause infections in people with weaker immunity: young children, older parents, anyone recovering from an illness. A warm, damp sponge full of food scraps is close to perfect living conditions for them.
The more unsettling finding was about cleaning. Sponges that their owners said they regularly sanitised, by boiling or microwaving, did not have fewer bacteria. They had a bigger share of the potentially harmful kinds, perhaps because the toughest ones survive and grow back quickly into the space left behind.
What actually helps - Change the sponge or scrubber every week or so. It is cheap. A stomach bug going round the family is not. - Squeeze it out after use and let it dry. Don't leave it sitting in a puddle by the sink. - Use one for dishes and a separate cloth for wiping the counter, so you are not spreading raw chicken juice across the slab. - Wash chopping boards and plates that held raw meat with hot soapy water, then let them dry fully. - Brushes and steel scrubbers dry faster and hold less than soft foam.
Where this comes from - Cardinale M et al. Microbiome analysis and confocal microscopy of used kitchen sponges reveal massive colonization by Acinetobacter, Moraxella and Chryseobacterium species. Scientific Reports, 2017.
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